Cold seal packages have openings that are sealed under the application of pressure without the need for the application of elevated temperatures. Cold seal packaging can be used to package a variety of goods, including comestibles, pharmaceuticals, and medical supplies. They typically utilize cold seal adhesives such as natural rubber (also referred to as latex rubber). Such cold seal adhesives are differentiated from heat seal adhesives in that heat seal adhesives typically require both elevated temperature and pressure for activation. Cold seal adhesives are used as an alternative in packaging because heat seal adhesives have limitations in manufacturing. For example, heat seal adhesives require additional time for thermal diffusion to activate them.
Natural rubber (or latex rubber) has several disadvantages. Of particular concern is that it can initiate an allergic response in people. It is believed that certain people become sensitized to allergens in natural rubber over repeated exposure to natural rubber and, thus, exhibit increasingly severe allergic responses upon each exposure. This is particularly significant in the medical area where both health care workers and chronically ill patients are repeatedly and directly exposed to products, such as natural rubber gloves, tubing, and the like. To a lesser extent, medical packaging for wound dressings and bandages may also contain natural rubber in the cold seal adhesives used in packaging. Other disadvantages of natural rubber include discoloration upon aging and an unpleasant odor.
Synthetic cold seal adhesives have been incorporated into packaging to overcome the disadvantages associated with natural rubber. For example, U.S. Pat. No. 4,442,259 (Isgur et al.) describes the use of aqueous based polyurethanes in cold seal packaging applications. U.S. Pat. No. 5,616,400 (Zhang) describes a cold seal adhesive for use in forming packages. The cold seal adhesive is formed from a polyurethane ionomer, wherein overlapping coatings of the cold seal adhesive are pressed together forming an envelope enclosing an item packaged. That is, the seal is formed between the same substrates and same adhesives with no difference in adhesion at the two interfaces between the layer of adhesive and the substrates.
While these patents have described the adhesive characteristics of these synthetic cold seal materials, the opening characteristics of packaging remain an important consideration. This is of particular concern in packaging pharmaceutical and medical supplies to maintain sterility within the package. Evidence of tampering or breach of the cold seal are important features of such packaging. However, a competing interest is also opening the bond formed in a package with a cold seal material. For example, it is desirable that the package be easily opened with controlled predictable motion and force resulting in a decreased likelihood of spillage of the package contents.
Thus, what is yet needed is a cold seal package which exhibits sufficient bond strength and yet is easily opened and preferably provides evidence of prior opening.
Methods for making a cold seal package and cold seal packages are provided by the present invention. A cold seal package generally includes constructions wherein two substrates, which can be two discrete portions of a contiguous sheet material, for example, are sealingly engaged to one another, preferably, to form a sealed enclosure for placement of an article therein. The two sealing portions of the substrate(s) can be generally easily and cleanly peeled apart without substantial damage to the substrate(s). Furthermore, the sealing portions of the substrate(s) cannot typically be resealed, or refastened, once peeled apart, thereby forming a substantially xe2x80x9cnon-refastenable cold seal.xe2x80x9d By this it is meant that after initially sealing, opening, and then again engaging the sealing portions of the substrate(s), a very small or nonexistent force would be required for reopening the package.
This non-refastenable cold seal can be formed, for example, between two sealing portions of the substrate(s) and two layers of contact adhesive, which may be the same or different. The bond formed at the interface of the two layers of contact adhesive is typically a substantially permanent bond (referred to herein as a cold seal bond or a cold seal adhesive bond). That is, upon opening the package of the present invention at the cold seal, the layers of adhesive are not separated from each other. The bond formed at the interface of a layer of the contact adhesive and one of the substrates (i.e., the anchor substrate) is also typically a permanent bond, whereas the bond formed at the interface of a layer of the contact adhesive and the other substrate (i.e., the transfer substrate) is a peelable and nonrefastenable bond. The bond at the interface of the layer of the contact adhesive and the transfer substrate is peelable as a result of a layer of a release coating on the surface of the transfer substrate. The peelability may result from release of the adhesive and the release coating from the transfer substrate, or portions thereof, or from release of just the adhesive with the release coating remaining on the transfer substrate.
In one embodiment, the present invention provides a method for making a cold seal package comprising the steps of: applying a first substantially natural latex rubber-free contact adhesive to an anchor surface to form an anchor contact adhesive coating; applying a release coating composition to a transfer surface to form a release-coated transfer surface; applying a second substantially natural latex rubber-free contact adhesive to the release-coated transfer surface to form a transfer contact adhesive coating; and contacting the anchor contact adhesive coating with the transfer contact adhesive coating, each of which are at a temperature of about 50xc2x0 C. or less, to form a substantially non-refastenable cold seal between the anchor surface and the release-coated transfer surface; wherein, upon peeling the anchor and transfer surfaces apart, substantially all of the anchor contact adhesive coating and the transfer contact adhesive coating that formed the cold seal remain on the anchor surface. It will be understood that there may be other portions of the transfer contact adhesive that were not used in forming the cold seal that remain on the transfer substrate depending on the coating patterns of the contact adhesive layers and release coating.
The first substantially natural latex rubber-free contact adhesive and the second substantially natural latex rubber-free contact adhesive may be the same contact adhesive or they may be different contact adhesives. Preferably, the contact adhesives have an open time of at least about 24 hours at a temperature of about 50xc2x0 C. or less. The first and second substantially natural latex rubber-free contact adhesives preferably each comprise a material selected from the group of a polychloroprene, a polyurethane, a styrene-isoprene copolymer, a styrene-butadiene copolymer, a polyimide, a polyvinyl chloride, a nitrocellulose, a polyisoprene, an acrylonitrile-butadiene-isoprene terpolymer, a butadiene-methacrylonitrile copolymer, a polyethylene-vinyl acetate copolymer, a polyacrylate, and mixtures thereof. Preferably, at least one of the first and second substantially natural latex rubber-free contact adhesives is formed from an aqueous polyurethane dispersion.
Preferably and advantageously for enhanced adhesion of the contact adhesive, the anchor surface is treated prior to applying the first substantially natural latex rubber-free contact adhesive. This step of treating the anchor surface preferably involves corona treating the anchor surface, although other treatment techniques can be used, such as flame treatment or coating with a primer, for example.
Upon applying the release coating composition to a transfer surface, preferably and advantageously, a substantially continuous release coating is formed. By this it is meant that the release coating includes few, if any, voids, for example. This substantially continuous release coating can be pattern coated or flood coated on the transfer surface, preferably, however, it is pattern coated. The release coating composition preferably comprises a release material selected from the group of an ethyl acrylate-acrylonitrile copolymer, an acrylic acid-alkyl acrylate copolymer, a polyvinyl chloride resin, a polyvinyl N-octadecyl carbamate, a polyethylene based wax, a polyamide based wax, a polysiloxane, a fluorocarbon polymer, a polyvinyl ester, a polyethylene imine, an alkyl substituted amine, a chromium complex, a fatty acid based wax, and mixtures thereof. The release coating composition can optionally also include a substantially natural latex rubber-free contact adhesive.
In certain embodiments of the method, the anchor surface and the transfer surface are on two separate substrates, as for example, when each comprises a first major surface of separate sheet materials. In other embodiments, however, the anchor surface and the transfer surface are on two different portions of the same substrate, as for example, a contiguous sheet material. When both surfaces are part of a contiguous sheet material, the anchor surface and the transfer surface may each be on a different portion of a first major surface of the sheet material. Alternatively, the anchor surface may be on a portion of a first major surface of the sheet material and the transfer surface may be on a second major surface of the sheet material.
Typically, in forming a package, the step of contacting the adhesive coatings to form a substantially non-refastenable cold seal produces an enclosure within the package. An article, preferably, a medical product such as a bandage, for example, is placed in the enclosure before completely sealing the package. Typically, when a medical product is placed inside the package, after sealing the package, the method includes a step of sterilizing the medical product. The method of the invention can also optionally include a step of printing graphic indicia on a substrate, such as on one of the separate sheet materials.
The present invention also provides a cold seal package comprising: an anchor substrate having a first major surface and a second major surface; a transfer substrate having a first major surface and a second major surface, wherein the first major surface of the transfer substrate has a release coating thereon to form a release-coated surface; and a substantially natural latex rubber-free contact adhesive disposed between the first major surface of the anchor substrate and the release coating of the release-coated surface of the transfer substrate forming a substantially non-refastenable cold seal between the anchor substrate and the transfer substrate; wherein adhesion between the contact adhesive and the first major surface of the anchor substrate is greater than adhesion between the contact adhesive and the release-coated transfer substrate. Preferably, substantially all of the substantially natural latex rubber-free contact adhesive remains on the first major surface of the anchor substrate upon opening a cold seal package by peeling the anchor substrate and transfer substrate apart. More preferably, at least a portion of the substantially continuous release coating also remains on the substantially natural latex rubber-free contact adhesive upon opening a cold seal package by peeling the anchor substrate and transfer substrate apart. Preferably, a cold seal package has a T-Peel Force between the release-coated transfer substrate and the substantially natural latex rubber-free contact adhesive of about 600 g/2.5 cm or less.
Preferably, in the package the anchor substrate and the transfer substrate each comprise a sheet material. Alternatively, the anchor substrate and the transfer substrate form different portions of the same substrate, such as a contiguous sheet material.
The anchor substrate and the transfer substrate can each have the same or a different substantially natural latex rubber-free contact adhesive coated thereon. Preferably, the substantially natural latex rubber-free contact adhesive can include two layers of different contact adhesives, one coated on each of the anchor substrate and the transfer substrate at a coating weight of about 4.0 g/m2 or less. Each can be pattern coated or flood coated, preferably, however, the contact adhesive layer adjacent the release coating is substantially contiguous with the transfer substrate. In this case, the substantially continuous release coating is pattern coated on the transfer substrate.
Another embodiment of the present invention is a cold seal package comprising: an anchor substrate having a first major surface and a second major surface; a transfer substrate having a first major surface and a second major surface, wherein the first major surface has a substantially continuous release coating thereon to form a release-coated surface; and a substantially natural latex rubber-free contact adhesive having an open time of at least about 24 hours-disposed between the first major surface of the anchor substrate and the release-coated surface of the transfer substrate, wherein a substantially non-refastenable cold seal is formed between the first major surface of the anchor substrate and the release coating of the release-coated surface of the transfer substrate such that adhesion between the contact adhesive and the first major surface of the anchor substrate is greater than adhesion between the contact adhesive and the release-coated transfer substrate.
As used herein, xe2x80x9cnon-refastenable cold sealxe2x80x9d means a seal formed between two substrates, which can be two portions of the same substrate such as two different portions of a contiguous sheet material, using an adhesive or combination of adhesives that can form a bond at room temperature (i.e., about 20xc2x0 C. to about 30xc2x0 C.). The peel strength of the non-refastenable cold seal of a package of the present invention is at least about 20 grams/2.5 centimeters (20 g/2.5 cm). Preferably, the non-refastenable cold seal has a peel strength of at least about 80 g/2.5 cm and is stable (i e., the seal does not fail) at temperatures typically encountered during transportation and delivery, which can be up to about 70xc2x0 C. This non-refastenable cold seal includes bonds formed at a number of interfaces, e.g., between an adhesive and an anchor substrate (typically, a permanent bond), between two layers of adhesive (typically, a permanent xe2x80x9ccold seal bondxe2x80x9d), between a release coating and a transfer substrate (optionally, a peelable bond), and between an adhesive and a release coating (optionally, a peelable bond).
As used herein, xe2x80x9cnatural latex rubberxe2x80x9d or xe2x80x9cnatural rubberxe2x80x9d means a milky fluid primarily obtained from the Heavea brasiliensis tree (also know as the rubber tree). Typically, the milky fluid contains small particles of naturally occurring substances, such as cis-1,4-polyisoprene, stabilized by proteins and dispersed in an aqueous medium.
As used herein, xe2x80x9csubstantially natural latex rubber-freexe2x80x9d refers to a contact adhesive composition to which natural rubber is not intentionally added. Preferably, the contact adhesive composition contains about 1 part per million (ppm) or less, and more preferably about 1 part per billion (ppb) or less, of a natural latex rubber and displays characteristics of a contact adhesive, as defined below.
As used herein, xe2x80x9ccontact adhesivexe2x80x9d (also known as a cold seal adhesive) is one that preferentially adheres to itself or a chemically similar material under pressure or force without the need for significantly elevated temperatures (e.g., without the need for temperatures above 50xc2x0 C.). Unlike pressure sensitive adhesives, contact adhesives are typically nonadhering or only very slightly adhering to chemically dissimilar surfaces at temperatures of about 15xc2x0 C. to about 50xc2x0 C. Thus, a contact adhesive preferably does not generally block, reseal, or stick to the contents placed inside the package. When placed against each other, contact adhesives typically require moderate pressure (such as that exerted by fingertip pressure) to achieve a bond without the application of significantly elevated temperatures. That is, packages may be sealed at room temperature (i.e., about 20xc2x0 C. to about 30xc2x0 C.) and even lower (e.g., 15xc2x0 C.), as well as at temperatures of up to about 50xc2x0 C., if the packaged product is not sensitive to such temperatures. The use of thermal curing or crosslinking agents in a contact adhesive are typically unnecessary to form a bond as is required in the formation of a xe2x80x9cheat seal.xe2x80x9d Heat seal adhesives typically require the application of high temperatures, generally at least about 100xc2x0 C., and often in a range of about 138xc2x0 C. to about 205xc2x0 C., in order to form a seal when the substrates are brought together. Thus, a contact adhesive (i.e., cold seal adhesive) as used herein is one that does not require elevated temperatures (i.e., above about 50xc2x0 C.) for activation of its adhesive characteristics. This includes, however, contact adhesives that can be hot melt coated, but that do not require the application of heat to form a seal.
Indeed, some suitable contact adhesives may be hot melt coated. When the contact adhesive is hot melt coated, it is tacky in the molten state (e.g., at a temperature of about 90xc2x0 C. to about 150xc2x0 C.) but is nonadhering or very slightly adhering to chemically dissimilar surfaces at a temperature of about 50xc2x0 C. or less, preferably at room temperature. Once the hot melt coated adhesive is cooled, a package is typically formed by bringing two adhesive-coated surfaces, which can be on two separate substrates or on the same substrate, together under moderate pressure, preferably at room temperature.
A contact adhesive is to be distinguished from a pressure sensitive adhesive (PSA). A PSA is typically tacky at room temperature, requires moderate pressure to achieve a bond (such as that exerted by fingertip pressure), but which adheres to a wide variety of dissimilar substrates. A pressure sensitive adhesive is conventionally understood to refer to an adhesive that displays permanent and aggressive tackiness to a wide variety of substrates after applying only light pressure. An accepted quantitative description of a pressure sensitive adhesive is given by the Dahlquist criterion line, which indicates that materials having a storage modulus (Gxe2x80x2) of less than about 3xc3x97105 Pascals (measured at 10 radians/second at room temperature, about 20xc2x0 C. to about 22xc2x0 C.) have pressure sensitive adhesive properties while materials having a Gxe2x80x2 in excess of this value do not.